Hydrogen is a promising clean energy fuel source. Hydrogen storage has been a challenging and critic technique for hydrogen fuel cell technology. Tremendous efforts have been devoted to the development of hydrogen storage materials including complex and chemical hydrides composed of light elements and with high hydrogen contents. Borohydrides, with high hydrogen contents have attracted considerable research attentions; however, they often encounter some critical problems for applications, for example, very slow reaction rates and unacceptably high reaction temperatures. More specifically, LiBH4 (˜18.4 wt %), its fully thermal decomposition is highly endothermic and requires high operation temperatures up to 320-900° C. A number of approaches have been adopted to improve the thermodynamic properties of hydrogen release from LiBH4 which are by reacting LiBH4 with chemicals such as SiO2, LiNH2, MgH2 and CaH2 etc. But the major hydrogen release needs relatively high temperatures (250-450° C.).
NH3 is also regarded as a hydrogen carrier due to its high hydrogen content and low liquefaction pressure. Nevertheless, given the state of “cracking” ammonia to hydrogen and nitrogen is an endothermic process, there are many issues in the on-board use of ammonia. Specifically, high operating temperature (>500° C.), longevity and reliability of catalysts and other components (at high temperatures and in the presence of impurities), purification requirements (to prevent ammonia poisoning of fuel cells), and etc.
Interesting results shown in a few recent investigations demonstrate that upon forming ammoniates, hydrogen can be produced through the interaction of NH3 with the host boron-containing hydrides. For instance, Mg(NH3)2(BH4)2 releases hydrogen in the temperature range of 150-400° C. with minor amount of NH3 (5-7 wt %). Protic H(N) and hydridic H(B) co-exist in the complex, where the strong potential in the combination of the oppositely charged H atoms to produce H2 and the establishment of strong B—N bond should be the driving forces for the dehydrogenation. It is, therefore, very interesting to investigate the dehydrogenation of a complex storage material comprises borohydride, ammonia and amide, since they are both high hydrogen content chemicals. Previous study reveals the thermal decomposition of lithium borohydride monoammoniate under a flow of inert gas can only give NH3 rather than H2. It is worthy of finding approaches to release hydrogen rather than NH3 from the system comprising lithium borohydride and ammonia. In the present invention, high-capacity of hydrogen can be released under mild conditions, from the hydrogen storage material comprising borohydride, ammonia and amide.